It cited the European Convention of Human Rights, a Poland-signatory treaty attached to the Strasbourg-based rights watchdog, the Council of Europe, on freedom of expression.

"This right protects not only information or ideas that are favourably received or regarded as inoffensive or as a matter of indifference, but also those that offend, shock or disturb," the commission said.

The statement comes amid a row in Poland over a heavy metal band called Behemoth.

Its lead singer, Adam Darski, while on stage in 2007, ripped up a Bible and called the Roman Catholic church a "murderous cult."

In a case with echoes of Pussy Riot in Russia or Mohammed cartoons in Denmark, the Polish supreme court on Monday said prosecutors can go after Darski on the basis of article 196 of Poland's penal code on "the crime of offending religious sensibilities."

In theory, he faces two years in prison. But nobody expects a jail sentence if he loses.

"[The decision] is negative and restricts the freedom of speech ... We are still arguing that we were dealing with art, which allows more critical and radical statements," Darski's lawyer, Jacek Potulski, told Reuters.

"The supreme court said clearly that there are limits for artists which cannot be crossed," Ryszard Nowak, a former MP for the right-wing Law and Justice opposition party, said on Polish TV.